Cells exposed to a cytotoxic compound can respond in a number of ways. If the insult is lethal, the cells may undergo necrosis, during which they lose membrane integrity and die rapidly, or the cells may follow another pathway of cell death, such as apoptosis or autophagy. Cells exposed to a sublethal insult may stop actively growing and dividing (a decrease in cell proliferation). Any of these responses can be measured individually or with multiplex assays to monitor whole cells or subcellular components or organelles. Parameters frequently measured—individually or in multiplex—include induction of superoxide, depletion of glutathione, decrease or loss of mitochondrial membrane potential, and reduction in overall viability.

Cytotoxicity assays are widely used in fundamental research and in drug discovery to screen libraries for toxic compounds. A compound generating a cytotoxic response may be eliminated from subsequent screening rounds; or, a compound targeting rapidly dividing cells may constitute a “hit” in a screen for cancer therapeutics. Many aspects of cytotoxicity can be assayed using reagents and assays from Thermo Fisher Scientific.

Viability assays

Cell viability can be assayed by parameters as diverse as the redox potential of the cell population, the integrity of cell membranes, or the activity of cellular enzymes such as esterases. These parameters each provide a different snapshot of cell health, and can individually or together form the basis of an assay for cell viability, cytotoxicity, or drug efficacy.

Cell proliferation assays

The analysis of cell proliferation is crucial for cell growth and differentiation studies as well as cancer research, and is often used to evaluate both compound toxicity and inhibition of tumor cell growth during drug development. Markers for measuring cell proliferation include average DNA content and cellular metabolism in a population. We have developed assays that report total cell number or total live cells, or provide single-cell indication of DNA synthesis.

Mitotoxicity assays

Mitochondrial function is an important parameter in cytotoxicity and can be monitored by measuring mitochondrial membrane potential, calcium flux, or reactive oxygen species. Probes for mitochondrial structure and function are often multiplexed to explore other cell health parameters and answer complex biological questions on cytotoxicity or drug efficacy using imaging, microplate, or flow cytometry platforms.

Lipotoxicity assays

Phospholipidosis and steatosis are toxic side effects of lipid metabolism that can be triggered by drugs or other compounds. Phospholipidosis is characterized by the accumulation of excess phospholipid complexes within the internal lysosomal membranes. Steatosis is the retention of lipids due to abnormal synthesis and elimination of triglyceride fats.

Cytotoxicity assay

Lactate dehydrogenase (LDH) is a cytosolic enzyme present in many different cell types. When the plasma membrane is damaged, LDH is released into the cell culture media. The Thermo Scientific Pierce™ LDH Cytotoxicity Assay Kit is a reliable colorimetric assay that can be used to quantitatively measure LDH released into the media from damaged cells as a biomarker for cellular cytotoxicity and cytolysis.